System and method for transmitting optical markers in a passive optical network system

ABSTRACT

In accordance with the teachings of the present invention, a system and method for transmitting optical markers in a passive optical network (PON) system is provided. In a particular embodiment, a method for transmitting optical markers in a PON system includes transmitting a first optical marker signal, the first optical marker signal used to identify at least one of the first optical marker signal, an upstream wavelength corresponding to the first optical marker signal, and an optical network unit (ONU) type transmitting at the upstream wavelength corresponding to the first optical marker signal. The method also includes transmitting a second optical marker signal, the second optical marker signal used to identify at least one of the second optical marker signal, an upstream wavelength corresponding to the second optical marker signal, and an ONU type transmitting at the upstream wavelength corresponding to the second optical marker signal. The method further includes, at a distribution node of the PON, routing the first optical marker signal to a first set of one or more optical fibers in a PON each corresponding to a first upstream wavelength and routing the second optical marker signal to a second set of one or more optical fibers in the PON each corresponding to a second upstream wavelength.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit under 35 U.S.C. §119(e) of U.S.Provisional Application Ser. No. 60/869,508 filed Dec. 11, 2006 by Boudaet al, and entitled System and Method for Transmitting Upstream WDMTraffic in a Passive Optical Network.

TECHNICAL FIELD

The present invention relates generally to communication systems and,more particularly, to a system and method for transmitting opticalmarkers in a passive optical network system.

BACKGROUND

In recent years, a bottlenecking of communication networks has occurredin the portion of the network known as the access network. Bandwidth onlonghaul optical networks has increased sharply through new technologiessuch as wavelength division multiplexing (WDM) and transmission oftraffic at greater bit rates. Metropolitan-area networks have also seena dramatic increase in bandwidth. However, the access network, alsoknown as the last mile of the communications infrastructure connecting acarrier's central office to a residential or commercial customer site,has not seen as great of an increase in affordable bandwidth. The accessnetwork thus presently acts as the bottleneck of communication networks,such as the internet.

Power-splitting passive optical networks (PSPONs) offer one solution tothe bottleneck issue. PSPONs refer to typical access networks in whichan optical line terminal (OLT) at the carrier's central office transmitstraffic over one or two downstream wavelengths for broadcast via aremote node (RN) to optical network units (ONUs). In the upstreamdirection, ONUs typically time-share transmission of traffic in onewavelength. An ONU refers to a form of access node that converts opticalsignals transmitted via fiber to electrical signals that can betransmitted to individual subscribers and vice versa.

PSPONs address the bottleneck issue by providing greater bandwidth atthe access network than typical access networks. For example, networkssuch as digital subscriber line (DSL) networks that transmit trafficover copper telephone wires typically transmit at a rate betweenapproximately 144 kilobits per second (Kb/s) and 1.5 megabits per second(Mb/s). Conversely, Broadband PONs (BPONs), which are example PSPONs,are currently being deployed to provide hundreds of megabits per secondcapacity shared by thirty-two users. Gigabit PONs (GPONs), anotherexample of a PSPON, typically operate at speeds of up to 2.5 gigabitsper second (Gb/s) by using more powerful transmitters, providing evengreater bandwidth. Other PSPONs include, for example, asynchronoustransfer mode PONs (APONs) and gigabit Ethernet PONs (GEPONs).

One current limitation of typical PSPONs is their limited reach. Reachgenerally refers to the maximum distance between the OLT and an ONU in aPON at which the OLT and the ONU can still communicate adequately. SinceONU transmitters are typically weaker than OLT transmitters, thelimiting factor in extending reach in a PON has primarily been in theupstream direction and not in the downstream direction. Many networkoperators desire a solution for extending reach in the upstreamdirection in a PON that can maintain the ratio of ONUs per OLT.

Some solutions that have been proposed to extend the reach in theupstream direction are to replace ONU transmitters with strongertransmitters, to add a more sensitive receiver at the OLT, or to useamplifiers to amplify upstream signals. These solutions have not beenparticularly persuasive in the marketplace. Cost considerations havedissuaded many operators from implementing stronger ONU transmitters ora more sensitive receiver at the OLT. Also, operators have viewedamplifiers as requiring costly maintenance and as creating a greaternumber of points of failure in a PON, decreasing the attractiveness ofsuch an option.

Yet another solution, a wavelength division multiplexing PON (WDMPON),would extend reach in the upstream (and downstream) direction. WDMPONsrefer to access networks in which each ONU receives and transmitstraffic over a dedicated downstream and upstream wavelength,respectively. In addition, each ONU is “colorless,” meaning that it isinterchangeable with any other ONU in any location in the PON. The powerloss experienced by a signal in the upstream direction in a WDMPON ismuch less than in a PSPON, thereby extending reach in the upstreamdirection. Although WDMPONs would extend reach in the upstreamdirection, they would do so at a prohibitively high cost for manyoperators and would provide reach far exceeding current or near-futuredemand.

Because demand for greater reach in the upstream direction continues togrow (but not at a rate to justify adoption of WDMPONs in most cases), aneed exists for cost-efficient solutions to extend the reach in PONs.

SUMMARY

One solution for extending the reach in a PON is to transmit upstreamtraffic at multiple wavelengths and route this traffic at a distributionnode of the PON through a multiplexer, as opposed to a power splitter.Typical multiplexers can properly receive traffic at a particular inputport in only a certain set of one or more wavelengths. Thus, for properupstream transmission to take place, each of the multiplexer's inputports should be connected to downstream ONUs that transmit at theappropriate wavelength (or set of wavelengths) for that input port. Onechallenge that network operators may face when implementing a PON thatroutes upstream WDM traffic through a multiplexer at the distributionnode is notifying whoever is deploying an ONU at a particular point inthe network about the type of ONU that should be deployed at that point(i.e., the ONU transmitting at the proper upstream wavelength).

In accordance with the teachings of the present invention, a system andmethod for transmitting optical markers in a passive optical network(PON) system is provided. In a particular embodiment, a method fortransmitting optical markers in a PON system includes transmitting afirst optical marker signal, the first optical marker signal used toidentify at least one of the first optical marker signal, an upstreamwavelength corresponding to the first optical marker signal, and anoptical network unit (ONU) type transmitting at the upstream wavelengthcorresponding to the first optical marker signal. The method alsoincludes transmitting a second optical marker signal, the second opticalmarker signal used to identify at least one of the second optical markersignal, an upstream wavelength corresponding to the second opticalmarker signal, and an ONU type transmitting at the upstream wavelengthcorresponding to the second optical marker signal. The method furtherincludes, at a distribution node of the PON, routing the first opticalmarker signal to a first set of one or more optical fibers in a PON eachcorresponding to a first upstream wavelength and routing the secondoptical marker signal to a second set of one or more optical fibers inthe PON each corresponding to a second upstream wavelength.

Technical advantages of one or more embodiments of the present inventionmay include extending the reach in the upstream direction in a PON. Byrouting upstream traffic using a multiplexer instead of a primary powersplitter at the RN, particular embodiments reduce the power lossexperienced by upstream traffic, thereby extending the reach in the PON.Also, particular embodiments include a single receiver at the OLT toreceive upstream traffic. By using a single receiver instead of multiplereceivers (as in a WDMPON) at the OLT, a demultiplexer need not be usedat the OLT. Not using a demultiplexer at the OLT reduces the power lossexperienced by upstream traffic, thereby further extending the reach inthe PON.

Another technical advantage of particular embodiments may includeincreasing upstream bandwidth in addition to extending reach in the PON.Particular embodiments may wavelength division multiplex upstreamtraffic. By doing so, these embodiments may transmit a larger amount ofupstream traffic in the PON at one time. The OLT may demultiplex thistraffic and receive the traffic in particular wavelengths at particularreceivers.

Yet another technical advantage of particular embodiments may includetransmitting optical markers downstream that indicate what type of ONUshould be installed at a particular location in the PON. Sinceparticular embodiments may require that only certain upstreamwavelengths be transmitted at certain locations in the PON, only ONUstransmitting at a particular wavelength may be installed at particularlocations in the PON. Transmitting optical markers downstream indicatingthe particular upstream wavelength that can be transmitted at aparticular location may allow the proper ONU to be installed at thatlocation. In particular embodiments, transmitting optical markersdownstream may be more cost-efficient than using “colorless” ONUs, as inWDMPON.

In addition, another technical advantage of particular embodiments mayinclude facilitating an upgrade in downstream capacity and reach byinstalling a PON architecture that can support both an upstream anddownstream increase in capacity and reach. Thus, particular embodimentsmay provide increased upstream reach (and, optionally, bandwidth) andmay be easily upgradeable (due to the architecture of the PON) toprovide increased downstream reach and bandwidth.

It will be understood that the various embodiments of the presentinvention may include some, all, or none of the enumerated technicaladvantages. In addition other technical advantages of the presentinvention may be readily apparent to one skilled in the art from thefigures, description, and claims included herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and itsfeatures and advantages, reference is now made to the followingdescription, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a diagram illustrating an example PSPON;

FIG. 2 is a diagram illustrating an example PSPON providing extendedreach in the upstream direction according to a particular embodiment ofthe invention;

FIG. 3 is a diagram illustrating an example HPON;

FIG. 4 is a diagram illustrating an example HPON providing extendedreach in the upstream direction according to a particular embodiment ofthe invention; and

FIG. 5 is a diagram illustrating an example PON system transmittingoptical markers downstream to indicate proper placement of ONUsaccording to a particular embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 is a diagram illustrating an example Power Splitting PassiveOptical Network (PSPON) 10. Typically, PSPONs have been employed toaddress the bottlenecking of communications networks in the portion ofthe network known as the access network. In recent years, bandwidth onlonghaul optical networks has increased sharply through new technologiessuch as wavelength division multiplexing (WDM) and transmission oftraffic at greater bit rates. In addition, metropolitan-area networkshave also seen a dramatic increase in bandwidth. However, the accessnetwork, also known as the last mile of the communicationsinfrastructure connecting a carrier's central office to a residential orcommercial customer site, has not seen as great of an increase inaffordable bandwidth. The access network thus presently acts as thebottleneck of communication networks, such as the internet.

PSPONs address the bottleneck issue by providing greater bandwidth atthe access network than typical access networks. For example, networkssuch as digital subscriber line (DSL) networks that transmit trafficover copper telephone wires typically transmit at a rate betweenapproximately 144 kilobits per second (Kb/s) and 1.5 megabits per second(Mb/s). Conversely, broadband PONs (BPONs) are currently being deployedto provide hundreds of megabits per second capacity shared by thirty-twousers. Gigabit PONs (GPONs), which typically operate at speeds of up to2.5 gigabits per second (Gb/s) by using more powerful transmitters,provide even greater bandwidth.

Referring back to PSPON 10 of FIG. 1, PSPON 10 includes an Optical LineTerminal (OLT) 12, optical fiber 30, a Remote Node (RN) 40, and OpticalNetwork Units (ONUs) 50. PSPON 10 refers to typical access networks inwhich an optical line terminal (OLT) at the carrier's central officetransmits traffic over one or two downstream wavelengths for broadcastto optical network units (ONUs). PSPON 10 may be an asynchronoustransfer mode PON (APON), a BPON, a GPON, a gigabit Ethernet PON(GEPON), or any other suitable PSPON. A feature common to all PSPONs 10is that the outside fiber plant is completely passive. Downstreamsignals transmitted by the OLT are passively distributed by the RN todownstream ONUs coupled to the RN through branches of fiber, where eachONU is coupled to the end of a particular branch. Upstream signalstransmitted by the ONUs are also passively forwarded to the OLT by theRN.

OLT 12, which may be an example of an upstream terminal, may reside atthe carrier's central office, where it may be coupled to a largercommunication network. OLT 12 includes a transmitter 14 operable totransmit traffic in a downstream wavelength, such as λ_(d), forbroadcast to all ONUs 50, which may reside at or near customer sites.OLT 12 may also include a transmitter 20 operable to transmit traffic ina second downstream wavelength λ_(v) (which may be added to λ_(d)) forbroadcast to all ONUs 50. As an example, in typical GPONs, λ_(v) maycarry analog video traffic. Alternatively, λ_(v) may carry digital datatraffic. OLT 12 also includes a receiver 18 operable to receive trafficfrom all ONUs 50 in a time-shared upstream wavelength, λ_(u). OLT 12 mayalso comprise filters 16 and 22 to pass and reflect wavelengthsappropriately.

It should be noted that, in typical PSPONs, downstream traffic in λ_(d)and λ_(v) is transmitted at a greater bit rate than is traffic in λ_(u),as PSPONs typically provide lower upstream bandwidth than downstreambandwidth. Also, downstream transmitters are typically more powerfulthan upstream transmitters, and thus, downstream reach is greater thanupstream reach. It should also be noted that “downstream” traffic refersto traffic traveling in the direction from the OLT (or upstreamterminal) to the ONUs (or downstream terminals), and “upstream” trafficrefers to traffic traveling in the direction from the ONUs (ordownstream terminals) to the OLT (or upstream terminal). It shouldfurther be noted that λ_(d) may include the band centered around 1490 m,λ_(v) may include the band centered around 1550 nm, and λ_(u) mayinclude the band centered around 1311 nm in particular PSPONs.

Optical fiber 30 may include any suitable fiber to carry upstream anddownstream traffic. In certain PSPONs 10, optical fiber 30 may comprise,for example, bidirectional optical fiber. In other PSPONs 10, opticalfiber 30 may comprise two distinct fibers.

RN 40 of PSPON 10 (which may also generally be referred to as adistribution node) comprises any suitable power splitter, such as anoptical coupler, and connects OLT 12 to ONUs 50. RN 40 is located in anysuitable location and is operable to split a downstream signal such thateach ONU 50 receives a copy of the downstream signal. Due to the splitand other possible power losses, each copy forwarded to an ONU has lessthan 1/N of the power of the downstream signal received by RN 40, whereN refers to the number of ONUs 50. In addition to splitting downstreamsignals, RN 40 is also operable to combine into one signal upstream,time-shared signals transmitted by ONUs 50. RN 40 is operable to forwardthe upstream signal to OLT 12.

ONUs 50 (which may be examples of downstream terminals) may include anysuitable optical network unit or optical network terminal (ONT) andgenerally refer to a form of access node that converts optical signalstransmitted via fiber to electrical signals that can be transmitted toindividual subscribers and vice versa. Subscribers may includeresidential and/or commercial customers. Typically, PONs 10 havethirty-two ONUs 50 per OLT 12, and thus, many example PONs may bedescribed as including this number of ONUs. However, any suitable numberof ONUs per OLT may be provided. ONUs 50 may include triplexers thatcomprise two receivers to receive downstream traffic (one for traffic inλ_(d) and the other for traffic in λ_(v)) and one transmitter totransmit upstream traffic in λ_(u). The transmission rate of the ONUtransmitter is typically less than the transmission rate of the OLTtransmitter (due to less demand for upstream capacity than fordownstream capacity). Also, the power of the ONU transmitter istypically less than the power of the OLT transmitter, and thus, upstreamreach is less than downstream reach. Each ONU 50 is operable to processits designated downstream traffic and to transmit upstream trafficaccording to an appropriate time-sharing protocol (such that the traffictransmitted by one ONU in λ_(u) does not collide with the traffic ofother ONUs in λ_(u)).

In operation, transmitter 14 of OLT 12 transmits downstream traffic forbroadcast to ONUs 50 in λ_(d). Transmitter 20 of OLT 12 may alsotransmit downstream analog video traffic for broadcast to ONUs 50 inλ_(v). Traffic in λ_(d) passes filter 16 and is combined with λ_(v) atfilter 22 (which passes λ_(d) and reflects λ_(v)). The combined trafficthen travels over optical fiber 30 to RN 40. RN 40 splits the downstreamtraffic into a suitable number of copies and forwards each copy to acorresponding ONU 50. Each ONU 50 receives a copy of the downstreamtraffic in λ_(d) and λ_(v) and processes the signal. Suitable addressingschemes may be used to identify which traffic is destined for which ONU50.

In the upstream direction, each ONU 50 may transmit upstream traffic inλ_(u) B along fiber 30 according to a suitable time-sharing protocol(such that upstream traffic does not collide). RN 40 receives theupstream traffic from each ONU 50 and combines the traffic from each ONU50 into one signal (at, e.g., the RN's power splitter). RN 40 thenforwards the combined traffic over fiber 30 to OLT 12. At OLT 12, thecombined traffic is passed by filter 22 and reflected by filter 16 toreceiver 18. Receiver 18 receives the signal and processes it.

One current limitation of typical PSPONs is their limited reach. Reachgenerally refers to the maximum distance between the OLT and an ONU in aPON at which the OLT and the ONU can still communicate adequately. SinceONU transmitters are typically weaker than OLT transmitters, thelimiting factor in extending reach in a PON has primarily been in theupstream direction and not in the downstream direction. Many networkoperators desire a solution for extending reach in the upstreamdirection in a PON.

One solution that has been proposed is to extend the reach in theupstream direction by either replacing ONU transmitters with strongertransmitters or by using amplifiers to amplify upstream signals. Neitherof these options has been persuasive in the marketplace. Costconsiderations have dissuaded many operators from implementing strongerONU transmitters. Also, operators have viewed amplifiers as requiringcostly maintenance and as creating a greater number of points of failurein a PON, decreasing the attractiveness of such an option.

Yet another solution, a wavelength division multiplexing PON (WDMPON),would extend reach in the upstream (and downstream) direction. WDMPONsrefer to access networks in which each ONU receives and transmitstraffic over a dedicated downstream and upstream wavelength,respectively. In addition, each ONU is “colorless,” meaning that it isinterchangeable with any other ONU in any location in the PON. The powerloss experienced by a signal in the upstream direction in a WDMPON ismuch less than in a PSPON, thereby extending reach in the upstreamdirection. Although WDMPONs would extend reach in the upstreamdirection, they would do so at a prohibitively high cost for manyoperators and would provide reach far exceeding current or near-futuredemand.

FIG. 2 is a diagram illustrating an example PSPON 400 providing extendedreach in the upstream direction according to a particular embodiment ofthe invention. To provide extended reach, ONUs 450 time-sharetransmission of upstream traffic in a plurality of wavelengths, λ₁-λ₄.RN 440 routes this upstream traffic through a multiplexer 446 (and notthrough primary power splitter 448). OLT 412 receives the traffic at oneor more receivers 418. By routing the upstream traffic throughmultiplexer 446 and not primary power splitter 448, the upstream trafficexperiences less power loss, thereby increasing the reach in theupstream direction.

PSPON 400 comprises OLT 412, optical fiber 430, RN 440, and ONUs 450.OLT 412 may reside at the carrier's central office, where it may becoupled to a larger communication network. OLT 412 includes transmitters414 and 420, receiver(s) 418, and filters 416 and 422. Transmitters 414and 420 may be the same as transmitters 14 and 20 described above inconjunction with FIG. 1 and thus will not be described again in detail.It should be noted that, in particular embodiments, OLT 412 may alsocomprise any suitable amplifier (not illustrated) operable to increasethe reach of downstream traffic.

Receiver(s) 418 comprise one or more suitable receivers operable toreceive traffic in λ₁-λ₄. In particular embodiments, ONUs 450, thoughtransmitting at four different wavelengths λ₁-λ₄, may time-sharetransmission of upstream traffic such that only a single ONU transmitsat a single wavelength during a particular time-slot. In suchembodiments, OLT 412 may include a single receiver operable to receivethe traffic in each time-slot, carried in any one of λ₁-λ₄. Althoughupstream bandwidth may not be increased in such embodiments, upstreamreach would be extended.

In alternative embodiments, an ONU 450 of two or more sets of ONUs 450a-450 d may transmit upstream traffic in the same time-slot at λ₁-λ₄,respectively, which may be multiplexed at multiplexer 446 of RN 440, asdescribed further below. In such embodiments, OLT 412 may include ademultiplexer (not illustrated) and multiple receivers corresponding toλ₁-λ₄. The demultiplexer may demultiplex λ₁-λ₄ and forward traffic ineach wavelength to a corresponding receiver. In such embodiments,upstream bandwidth would be increased, and upstream reach would beextended. However, since upstream traffic may lose additional power atthe demultiplexer in OLT 412, upstream reach may not be as great as inthe case where a single receiver is used at OLT 412 (and traffic inλ₁-λ₄ is not transmitted in the same time-slot).

It should be noted that, in particular embodiments, λ₁-λ₄ may comprisefixed sub-bands of λ_(u). In alternative embodiments, λ₁-λ₄ may compriseany other suitable wavelengths. It should further be noted thatreceiver(s) 418 may comprise one or more non-discriminating, spectrallybroadband receivers in particular embodiments. It should further benoted that, in particular embodiments, any suitable number of upstreamwavelengths may be transmitted, including, for example, a uniqueupstream wavelength for each ONU 650 (and PSPON 400 may be modified inany suitable manner to support such transmission).

Filter 416 is operable to receive the traffic in λ_(d) from transmitter414 and direct the traffic to filter 422. In the upstream direction,filter 416 is operable to receive the traffic in any one or more ofλ₁-λ₄ from filter 422 and direct the traffic to receiver(s) 418. Filter422 is operable to receive the traffic in λ_(d) from filter 416 and thetraffic in λ_(v) from transmitter 420, combine the traffic, and forwardthe traffic to RN 440. In the upstream direction, filter 422 is operableto receive the traffic in any one or more of λ₁-λ₄ from RN 440 anddirect the traffic to filter 416.

Optical fiber 430 may comprise any suitable fiber to carry upstream anddownstream traffic. In particular embodiments, optical fiber 430 maycomprise, for example, bidirectional optical fiber. In alternativeembodiments, optical fiber 430 may comprise two distinct fibers.

RN 440 comprises filter 442, multiplexer 446, primary power splitter448, and secondary power splitters 449. In the downstream direction, RN440 is operable to receive traffic in λ_(d) and λ_(v), split the trafficinto a plurality of copies at primary power splitter 448, and forwardeach copy to a particular ONU 450. In the upstream direction, RN 440 isoperable to receive the traffic in λ₁-λ₄ at multiplexer 446 and forwardthis traffic to OLT 412.

It should be noted that, in alternative embodiments, RN 440 may compriseany other suitable component(s) operable to route the trafficappropriately. For example, in particular embodiments, a single opticaldevice may split and multiplexed traffic (e.g., based on arrayedwaveguide grating (AWG) technology). It should also be noted thatalthough RN 440 is referred to as a remote node, “remote” refers to RN440 being communicatively coupled to OLT 412 and ONUs 450 in anysuitable spatial arrangement. A remote node may also generally bereferred to as a distribution node.

Filter 442 may comprise any suitable filter operable to receive adownstream signal from OLT 412 comprising traffic in λ_(d) and λ_(v) anddirect the signal to primary power splitter 448. In the upstreamdirection, filter 442 is operable to receive the traffic in λ₁-λ₄ fromprimary power splitter 448 and terminate the traffic. Filter 442 is alsooperable to receive the traffic in λ₁-λ₄ from multiplexer 446 and directthe traffic to OLT 412. Filter 442 is operable to forward the traffic inλ₁-λ₄ from multiplexer 446, but not the traffic in λ₁-λ₄ from primarypower splitter 448. Although filter 442 includes only one filter in theillustrated embodiment, in alternative embodiments, filter 442 maycomprise any suitable number of filters (coupled to optional switches)to facilitate an upgrade of the network.

Multiplexer 446 may comprise any suitable multiplexer/demultiplexer (andmay be considered a wavelength router) and is operable to receiveupstream traffic in one or more of wavelengths λ₁-λ₄ from secondarypower splitters 449 a-449 d, respectively, and forward the traffic tofilter 442. In particular embodiments, where upstream transmission isbeing time-shared such that only a single ONU transmits at a singlewavelength during a particular time-slot, multiplexer 446 receives thetraffic in the single wavelength in the particular time-slot from acorresponding secondary power splitter 449 and forwards the traffic tofilter 442. In alternative embodiments, where an ONU from two or moresets of ONUs 450 a-450 d transmits at one of λ₁-λ₄, respectively, duringa particular time-slot, multiplexer 446 is operable to receive thetraffic in the multiple wavelengths in the particular time-slot from acorresponding set of secondary power splitters 449, multiplex thewavelengths into one signal, and forward the signal to filter 442.

In the illustrated embodiment, multiplexer 446 receives upstream trafficin λ₁-λ₄ at ports one through four, respectively, from secondary powersplitters 449 a-449 d, respectively. However, it should be noted that,in alternative embodiments, multiplexer 446 may receive upstream trafficin any other suitable number of wavelengths and at any suitable set ofports. For example, in particular embodiments, multiplexer 446 maycomprise a cyclic multiplexer or a multiplexer with a greater number ofports. Also, although one multiplexer 446 is illustrated in remote node440 of FIG. 2, in alternative remote nodes, multiplexer 446 may comprisetwo or more separate multiplexers receiving upstream signals from one ormore downstream sources and forwarding the traffic upstream.

Primary power splitter 448 may comprise any suitable power splitter,such as an optical coupler, operable to receive downstream traffic inλ_(d) and λ_(v) and split the traffic into four copies. The power ofeach copy may be less than one-fourth of the power of the originalsignal. Primary power splitter 448 is operable to forward each copy to acorresponding secondary power splitter 449 a-449 d. In the upstreamdirection, primary power splitter 448 is operable to receive traffictransmitted by ONUs 450 over λ₁-λ₄ from secondary power splitters 449a-449 d, respectively, and combine this traffic into one signal. Primarypower splitter 448 is further operable to forward this signal to filter442 for termination. Although primary power splitter 448 comprises a 1×4power splitter in the illustrated embodiment, any other suitable powersplitter may be used in alternative embodiments.

Each secondary power splitter, one of 449 a-449 d, may comprise anysuitable power splitter, such as an optical coupler, operable to receivea copy of downstream traffic in λ_(d) and λ_(v) from primary powersplitter 448, split the copy into a suitable number of copies, andforward each resulting copy to an ONU in a corresponding set ofdownstream ONUs 450. In the upstream direction, each secondary powersplitter 449 is operable to receive traffic transmitted at one of λ₁-λ₄from each ONU 450 of a corresponding set of downstream ONUs 450 andcombine the traffic from each ONU 450 into one signal. For example,secondary power splitter 449 a is operable to receive traffictransmitted at time-shared λ₁ from ONUs 450 a, secondary power splitter449 b is operable to receive traffic transmitted at time-shared λ₂ fromONUs 450 b, secondary power splitter 449 c is operable to receivetraffic transmitted at time-shared λ₃ from ONUs 450 c, and secondarypower splitter 449 d is operable to receive traffic transmitted attime-shared λ₄ from ONUs 450 d.

Each secondary power splitter 449 is operable to split the combinedupstream traffic into two copies and forward one copy to primary powersplitter 448 and one copy to a corresponding port of multiplexer 446.The copy forwarded to primary power splitter 448, as described above,may be combined with other traffic from other ONUs 450 (and laterterminated). The copy forwarded to multiplexer 446 may be forwarded bymultiplexer 446 to filter 442 and directed to OLT 412. Althoughsecondary power splitters 449 comprise 2×4 couplers in the illustratedembodiment, in alternative embodiments, secondary power splitters 449may comprise any suitable couplers or combination of couplers, such as,for example, a 2×2 coupler coupled to two 1×2 couplers. Also, secondarypower splitters 449 may split or combine any suitable number of signals.

Each ONU 450 (which may be an example of a downstream terminal) maycomprise any suitable ONU or ONT. Each ONU 450 comprises a filter 460,receiver 462, filter 470, receiver 472, and transmitter 482. Each filter460 may comprise any suitable filter operable to direct downstreamtraffic in λ_(v) to receiver 462. Filter 460 is also operable to passthe traffic in λ_(d) to filter 470 and to pass the upstream traffic in acorresponding one of λ₁-λ₄ to RN 440. Receiver 462 may comprise anysuitable receiver operable to receive the traffic in λ_(v) and toprocess the traffic. Each filter 470 may comprise any suitable filteroperable to receive the traffic in λ_(d) and direct it to receiver 472.Filter 470 is also operable to pass the upstream traffic in acorresponding one of λ₁-λ₄ to a corresponding filter 460. Receiver 472may comprise any suitable receiver operable to receive the traffic inλ_(d) and process the traffic.

Each transmitter 482 may comprise any suitable transmitter operable totransmit traffic at a corresponding one of λ₁-λ₄ in the upstreamdirection. Transmitters 482 a of ONUs 450 a time-share transmission atλ₁, transmitters 482 b of ONUs 450 b time-share transmission at λ₂ (notillustrated), transmitters 482 c of ONUs 450 c time-share transmissionat λ₃ (not illustrated), and transmitters 482 d of ONUs 450 d time-sharetransmission at λ₄. As discussed above, all ONUs 450 may time-sharetransmission in particular embodiments such that only a single ONU 450transmits at a single wavelength at a particular time-slot. Inalternative embodiments, an ONU 450 a, an ONU 450 b, an ONU 450 c,and/or an ONU 450 d may transmit at λ₁-λ₄, respectively, in the sametime-slot.

It should be noted that although four ONUs 450 are illustrated as beingpart of a group of ONUs 450 sharing an upstream wavelength in PSPON 400,any suitable number of ONUs 450 may be part of a group sharing anupstream wavelength. It should also be noted that any suitable number ofONUs 450 may be implemented in the network. It should further be notedthat, in particular embodiments, only those ONUs 450 transmitting at aparticular wavelength may be placed downstream of a particular port atmultiplexer 446 of RN 440. Otherwise, the multiplexer port will notdirect the wavelength properly.

In operation, in the downstream direction, transmitters 414 and 420 atOLT 412 transmit traffic at λ_(d) and λ_(v), respectively. Filter 416receives the traffic in λ_(d) and forwards the traffic to filter 422.Filter 422 receives the traffic in λ_(d) and λ_(v), combines the trafficinto one signal, and forwards the signal over fiber 430 to RN 440.Filter 442 of RN 440 receives the traffic in λ_(d) and λ_(v) and directsthe traffic to primary power splitter 448. Primary power splitter 448receives the traffic in λ_(d) and λ_(v), splits the traffic into fourcopies, and forwards each copy to a corresponding secondary powersplitter 449. Each secondary power splitter 449 receives a copy of λ_(d)and λ_(v), splits the copy into four copies, and forwards each resultingcopy to an ONU 450 in a corresponding set of downstream ONUs 450. Eachfilter 460 receives a corresponding copy of traffic in λ_(d) and λ_(v),directs the traffic in λ_(v) to a corresponding receiver 462, anddirects the traffic in λ_(d) to a corresponding filter 470. Receiver 462receives the traffic in λ_(v) and processes the traffic. Filter 470receives the traffic in λ_(d) and directs it to a corresponding receiver472. Receiver 472 receives the traffic in λ_(d) and processes thetraffic.

In the upstream direction, sets of ONUs 450 a-450 d transmit at λ₁-λ₄,respectively. In particular embodiments, as described above, only asingle ONU 450 transmits traffic in a particular time-slot (and all ofONUs 450 time-share time-slots), thereby increasing reach. Inalternative embodiments, an ONU of one or more sets of ONU 450 a-450 dtransmits in a particular time-slot (and ONUs of each set time-sharetime-slots), thereby increasing reach and upstream bandwidth. Thus, inthese embodiments, ONUs 450 a time-share transmission at λ₁, ONUs 450 btime-share transmission at λ₂ (not illustrated), ONUs 450 c time-sharetransmission at λ₃ (not illustrated), and ONUs 450 d time-sharetransmission at λ₄.

Secondary power splitters 449 a-449 d receive the traffic in λ₁-λ₄,respectively. Each secondary power splitter 449 splits the receivedtraffic into two copies and forwards one copy to multiplexer 446 and onecopy to primary power splitter 448. Multiplexer 446 receives traffic inλ₁ at a first input port from secondary power splitter 449 a, traffic inλ₂ at a second input port from secondary power splitter 449 b (notillustrated), traffic in λ₃ at a third input port from secondary powersplitter 449 c (not illustrated), and traffic in λ₄ at a fourth inputport from secondary power splitter 449 d. In the embodiments in which asingle ONU 450 transmits per time-slot, multiplexer 446 receives thetraffic and forwards the traffic to filter 442. In the embodiments inwhich ONUs 450 transmit at λ₁-λ₄ (or a subset of λ₁-λ₄) per time-slot,multiplexer 446 receives the traffic, combines the traffic, and forwardsthe traffic to filter 442. Primary power splitter 448 receives trafficin λ₁-λ₄ from secondary power splitters 449, combines the traffic intoone signal (when traffic in a plurality of λ₁-λ₄ is transmitted pertime-slot), and forwards the traffic to filter 442. Filter 442 receivesthe traffic in the particular set of λ₁-λ₄ from multiplexer 446 anddirects the traffic to OLT 412 over fiber 430. Filter 442 also receivesthe traffic in the particular set of λ₁-λ₄ from primary power splitter448 and terminates the traffic in any suitable manner.

Filter 422 of OLT 412 receives the traffic in the particular set ofλ₁-λ₄ and directs the traffic to filter 416. In the embodiments in whicha single ONU 450 transmits per time-slot, filter 416 receives thetraffic in the particular one of λ₁-λ₄ and directs the traffic toreceiver 418. In the embodiments in which ONUs 450 transmit at two ormore of λ₁-λ₄ per time-slot, filter 416 receives the traffic in theparticular set of two or more wavelengths and forwards the traffic to ademultiplexer (not illustrated). The demultiplexer demultiplexes thewavelengths and forwards the traffic in each wavelength to acorresponding receiver 418. Receiver(s) 418 receive the traffic andprocess it.

Modifications, additions, or omissions may be made to the examplesystems and methods described without departing from the scope of theinvention. The components of the example methods and systems describedmay be integrated or separated according to particular needs. Moreover,the operations of the example methods and systems described may beperformed by more, fewer, or other components.

As described above, PSPON 400 may decrease the power loss experienced byupstream traffic by routing the traffic at RN 440 through multiplexer446 (which may generate relatively little to no insertion loss inparticular embodiments) and not primary power splitter 448 (which maygenerate greater than six decibels of insertion loss in particularembodiments). By decreasing the power loss experienced by upstreamtraffic, PSPON 400 provides extended reach. Also, PSPON 400 may provideincreased upstream bandwidth in particular embodiments.

Extended upstream reach and, optionally, increased upstream bandwidthcan also be provided in hybrid PONs (HPONs), which are hybrids betweenPSPONs and WDMPONs in the downstream direction. FIG. 3 illustrates anexample HPON, and FIG. 4 illustrates an example HPON providing extendedupstream reach and, optionally, increased upstream bandwidth.

FIG. 3 is a diagram illustrating an example HPON 500. Example HPON 500comprises OLT 512, optical fiber 530, RN 540, and ONUs 550. Example HPON500 provides greater downstream capacity than a PSPON by having groupsof two or more ONUs 550 share downstream WDM wavelengths. It should benoted that an HPON generally refers to any suitable PON that is not afull WDMPON but that is operable to route downstream traffic inparticular wavelengths to particular ONUs (and to transmit upstreamtraffic in any suitable manner). An HPON may include both an HPON thattransmits downstream traffic in a plurality of wavelengths each sharedby a group of wavelength-sharing ONUs (a WS-HPON, as is illustrated) andan HPON that transmits downstream traffic in a unique wavelength foreach ONU (retaining PSPON characteristics in the upstream direction).

OLT 512 (which may be an example of an upstream terminal) may reside atthe carrier's central office and comprises transmitters 514, multiplexer515, filter 516 and receiver 518, and transmitter 520 and filter 522.Each transmitter 514 a-514 d may comprise any suitable transmitter andis operable to transmit traffic over a corresponding wavelength, λ₁-λ₄,respectively.

It should be noted that, λ₁-λ₄ are used in HPON 500 for illustrativepurposes only and need not represent the same wavelengths as λ₁-λ₄ ofPSPON 400, described above. Also, although four transmitters areillustrated in example HPON 500, any suitable number of transmitters maybe included, transmitting traffic at any suitable number of wavelengths.It should also be noted that although example HPON 500 does not provideWDM for upstream traffic, it may be economical to implement transceivers(transmitter and receiver) in OLT 512, instead of only transmitters 514,in anticipation of a further upgrade to WDM upstream (e.g., an upgradeto particular embodiments of HPON 600 of FIG. 4).

Multiplexer 515 comprises any suitable multiplexer/demultiplexer (andmay be considered a wavelength router) and is operable to combine thetraffic in λ₁-λ₄ into one signal. In particular example networks,multiplexer 515 may comprise a cyclic multiplexer operable to receiveand combine the traffic in more than one wavelength through each port.In other example networks, multiplexer 512 may be a typical N×1multiplexer operable to receive only the traffic in one wavelengththrough each port.

Filter 516 comprises any suitable filter operable to receive the trafficin λ₁-λ₄ from multiplexer 515 and pass the traffic in λ₁-λ₄ to filter522. In the upstream direction, filter 516 is operable to receivetraffic in λ_(u) and direct traffic in λ_(u) to receiver 518. Receiver518 may comprise any suitable receiver operable to receive and processupstream traffic from ONUs 550 carried over time-shared λ_(u).

Transmitter 520 comprises any suitable transmitter and is operable totransmit traffic over λ_(v) for eventual broadcast to all ONUs 550.Transmitter 520 is further operable to direct the traffic to filter 522.In particular embodiments, transmitter 520 may transmit analog videotraffic over λ_(v). In alternative embodiments, transmitter 520 maytransmit digital data traffic. It should be noted that, although asingle transmitter 520 is illustrated, OLT 512 may comprise any suitablenumber of transmitters operable to transmit traffic for eventualbroadcast to all ONUs 550.

Filter 522 is operable to receive the traffic in λ_(v) and the trafficin λ₁-λ₄ and combine the traffic. Filter 522 is also operable to directthe combined traffic over fiber 530 to RN 540. In the upstreamdirection, filter 522 is operable to receive traffic in λ_(u) and directthe traffic in λ_(u) to filter 516.

Optical fiber 530 may comprise any suitable fiber to carry upstream anddownstream traffic. In certain HPONs 500, optical fiber 530 maycomprise, for example, bidirectional optical fiber. In other HPONs 500,optical fiber 530 may comprise two distinct fibers, one carryingdownstream traffic and the other carrying upstream traffic.

RN 540 comprises filter 542, multiplexer 546, primary power splitter548, and secondary power splitters 549. RN 540 is operable to receivethe traffic in λ₁-λ₄ and λ_(v) from OLT 512, filter out and broadcastthe traffic in λ_(u), and demultiplex and forward the traffic in λ₁-λ₄to the ONUs in corresponding groups of wavelength-sharing ONUs 550. RN540 is further operable to receive from ONUs 550 upstream signalscarried over time-shared wavelength λ_(u), combine these signals, andforward the combined traffic in λ_(u) to OLT 512. It should be notedthat although RN 540 is referred to as a remote node, “remote” refers toRN 540 being communicatively coupled to OLT 512 and ONUs 550 in anysuitable spatial arrangement. A remote node may also generally bereferred to as a distribution node.

Filter 542 may comprise any suitable filter operable to receive a signalcomprising traffic in λ₁-λ₄ and λ_(v), pass the traffic in λ₁-λ₄ tomultiplexer 546, and direct the traffic in λ_(v) to primary powersplitter 548. Although filter 542 in the illustrated example includesonly one filter, filter 542 may comprise any suitable number of filters(coupled to optional switches) to facilitate an upgrade of the network.In the upstream direction, filter 542 is operable to receive the trafficin λ_(u) and direct it toward OLT 512.

Multiplexer 546 may comprise any suitable multiplexer/demultiplexer (andmay be considered a wavelength router) and is operable to receive thesignal comprising the traffic in λ₁-λ₄ and demultiplex the signal. Eachoutput port of multiplexer 546 is operable to forward the traffic in acorresponding one of λ₁-λ₄ to a corresponding secondary power splitter549 a-549 d, respectively. In the upstream direction, multiplexer 546 isoperable to receive and terminate the traffic in λ_(u), as ONUs 550 ofexample HPON 500 time-share λ_(u) (and do not transmit traffic overmultiple upstream wavelengths). Alternatively, multiplexer 546 mayforward this traffic to filter 542 for suitable termination (wheretermination may be performed internally or externally).

It should be noted that multiplexer 546 may comprise a cyclicmultiplexer or any other suitable type of multiplexer and may have anysuitable number of ports. Also, although one multiplexer 546 isillustrated in remote node 540 of FIG. 3, in alternative remote nodes,multiplexer 546 may comprise two or more separate multiplexers receivingdownstream signals from one or more upstream sources and forwarding thetraffic downstream such that ONUs 550 share wavelengths. It shouldfurther be noted that the traffic in each wavelength may pass to adifferent secondary power splitter than that illustrated, the traffic inmore than one wavelength may pass to a secondary power splitter, and/ormultiplexer 546 may receive, multiplex, and pass traffic in less or morethan four downstream wavelengths.

Primary power splitter 548 may comprise any suitable power splitteroperable to receive the traffic in λ_(v) and split the traffic into fourcopies. The power of each copy may be less than one-fourth of the powerof the original signal λ_(v). Primary power splitter 548 is operable toforward each copy to a corresponding secondary power splitter 549. Inthe upstream direction, primary power splitter 548 is operable toreceive traffic transmitted by ONUs 550 over time-shared λ_(u) fromsecondary power splitters 549 and combine this traffic into one signal.Primary power splitter 548 forwards the upstream signal to OLT 512.Primary power splitter 548 thus broadcasts the traffic in λ_(v) in thedownstream direction and combines traffic over time-shared λ_(u) in theupstream direction. Although primary power splitter 548 is illustratedas a 1×4 power splitter, any suitable power splitter may be used.

Each secondary power splitter 549 may comprise any suitable powersplitter, such as an optical coupler, operable to receive a signal fromprimary power splitter 548 and a signal from multiplexer 546, combinethe two signals into one signal, split the combined signal into asuitable number of copies, and forward each copy to the ONUs in acorresponding wavelength-sharing group of ONUs 550 (each group ofwavelength-sharing ONUs shares one of λ₁-λ₄ in the downstreamdirection). In the upstream direction, each secondary power splitter 549is operable to receive traffic transmitted at λ_(u) from each ONU 550 ofa corresponding group of ONUs 550 and combine the traffic from each ONU550 into one signal. Each secondary power splitter 549 is operable tosplit the combined upstream traffic into two copies and forward one copyto primary power splitter 548 and one copy to multiplexer 546. The copyforwarded to primary power splitter 548, as described above, is combinedwith other traffic from other ONUs 550 transmitted over time-sharedλ_(u). The copy forwarded to multiplexer 546 may be blocked or forwardedto filter 542 for suitable termination. Although secondary powersplitters 549 are illustrated as 2×4 couplers in example HPON 500,secondary power splitters 549 may be any suitable coupler or combinationof couplers (such as a 2×2 coupler coupled to two 1×2 couplers).Secondary power splitters 549 may split or combine any suitable numberof signals.

Each ONU 550 (which may be an example of a downstream terminal) maycomprise any suitable ONU or ONT. Each ONU 550 comprises a filter 560,receiver 562, filter 570, receiver 572, and transmitter 582. Each filter560 may comprise any suitable filter operable to direct traffic inwavelength λ_(v) (for example, analog video traffic) to receiver 562.Filter 560 is further operable to pass the traffic in the correspondingone of λ₁-λ₄ received at the ONU 550 to filter 570 and to pass thetraffic in λ_(u) to RN 540 in the upstream direction. Receiver 562 maycomprise any suitable receiver operable to receive the traffictransmitted in λ_(v) and process the traffic. Each filter 570 maycomprise any suitable filter operable to receive the traffic in acorresponding one of λ₁-λ₄ and direct it to receiver 572. Filter 570 isfurther operable to pass the traffic in upstream wavelength λ_(u) tocorresponding filter 560 in the upstream direction. Receiver 572 maycomprise any suitable receiver operable to receive the traffictransmitted in a corresponding one of λ₁-λ₄ and process the traffic.Receiver 572 may be operable to receive traffic in any one of λ₁-λ₄,providing flexibility in assigning (or re-assigning) an ONU 550 to aparticular wavelength-sharing group. Each transmitter 582 may compriseany suitable transmitter operable to transmit traffic over λ_(u) in theupstream direction, applying a suitable protocol to time-share λ_(u)with the other ONUs 550.

It should be noted that although four ONUs 550 are illustrated as beingpart of a group of ONUs 550 in HPON 500, any suitable number of ONUs 550may be part of a group sharing a downstream wavelength. In addition,there may be multiple groups each sharing a different downstreamwavelength. For example, ONUs 550 a may share λ₁, ONUs 550 b (notillustrated) may share λ₂, ONUs 550 c (not illustrated) may share λ₃,and ONUs 550 d may share λ₄. Also, one or more ONUs 550 may be a part ofmore than one group in some networks. It should also be noted that anysuitable number of ONUs 550 may be implemented in the network.

In operation, transmitters 514 a-514 d of OLT 512 transmit traffic atλ₁-λ₄, respectively, and forward the traffic to multiplexer 515.Multiplexer 515, which may include, for example, a cyclic multiplexer,combines the traffic in the four wavelengths into one signal andforwards the signal to filter 516. Filter 516 passes the downstreamsignal to filter 522. Transmitter 20 of OLT 512 also transmits trafficat λ_(v) and forwards the traffic to filter 522. Filter 522 receives thetraffic in λ₁-λ₄ and λ_(v) and directs the traffic over optical fiber530 to RN 540.

Filter 542 of RN 540 receives the signal and directs the traffic in(e.g., analog video) wavelength λ_(v) to primary power splitter 548,allowing the traffic in λ₁-λ₄ to pass to multiplexer 546. Primary powersplitter 548 receives the traffic in λ_(v) and splits it into a suitablenumber of copies. In the illustrated embodiment, primary power splitter548 splits the traffic in λ_(v) into four copies, and forwards each copyto a corresponding secondary power splitter 549. Multiplexer 546receives the signal comprising the traffic in λ₁-λ₄ and demultiplexesthe signal into its constituent wavelengths. Multiplexer 546 thenforwards the traffic in each wavelength along a corresponding fiber suchthat each secondary power splitter 549 receives the traffic in acorresponding one of λ₁-λ₄.

Each secondary power splitter 549 thus receives a copy of traffic inλ_(v) from primary power splitter 548 and traffic in a corresponding oneof λ₁-λ₄ from multiplexer 546, combines the traffic into one signal, andsplits the signal into a suitable number of copies. In the illustratedembodiment, each secondary power splitter 549 splits the signal intofour copies. In this way, the traffic (e.g., analog video) in wavelengthλ_(v) is broadcast to all ONUs 550 and a corresponding one of λ₁-λ₄ istransmitted to and shared by one or more groups of ONUs 550. In theillustrated embodiment, ONUs 550 a share λ₁, ONUs 550 b (notillustrated) share λ₂, ONUs 550 c (not illustrated) share λ₃, and ONUs550 d share λ₄. It should be noted again that the groups of ONUs 550sharing a wavelength may be different than those illustrated in FIG. 3,and groups of wavelength-sharing ONUs 550 may share more than one WDMwavelength in alternative networks.

After secondary power splitters 549 split the signal comprising thetraffic in a corresponding one of λ₁-λ₄ and the traffic in λ_(v) intofour copies, secondary power splitters 549 forward each copy over fiber530 such that the ONUs 550 coupled to the secondary power splitter 549receive a copy. Filter 560 of each ONU 550 receives the signal anddirects the traffic in λ_(v) to receiver 562, which then processes thetraffic carried over λ_(v). Filter 560 passes the corresponding one ofλ₁-λ₄ to filter 570. Filter 570 receives the traffic in thecorresponding one of λ₁-λ₄ and directs the traffic to receiver 572 whichthen processes the traffic. Again, since each ONU 550 in a group mayshare one of λ₁-λ₄ with other ONUs 550 in the group, ONUs 550 may applya suitable addressing protocol to process downstream trafficappropriately (e.g., to determine which portion of the traffictransmitted in the corresponding wavelength is destined for which ONU550 in a group).

In the upstream direction, transmitter 582 of each ONU 550 transmitstraffic over λ_(u). Filters 570 and 560 receive the traffic in λ_(u) andpass the traffic. The signal travels over fiber 530 to RN 540. Eachsecondary power splitter 549 of RN 540 receives traffic over time-sharedλ_(u) and combines the traffic from each ONU 550 in the correspondinggroup of ONUs 550. Again, since each ONU 550 transmits traffic overupstream wavelength λ_(u), ONUs 550 may adhere to a suitable protocol totime-share λ_(u) such that traffic from multiple ONUs 550 does notcollide. After receiving and combining traffic over λ_(u) into onesignal, each secondary power splitter 549 splits the signal into twocopies, forwarding one copy to multiplexer 546 and one copy to primarypower splitter 548. As discussed above, multiplexer 546 of examplenetwork 500 may block λ_(u) or forward λ_(u) to filter 542 for suitabletermination (internal or external to filter 542). Primary power splitter548 receives traffic over λ_(u) from each secondary power splitter 549,combines the traffic, and forwards the traffic to filter 542. Filter 542receives the combined traffic in λ_(u) and directs the traffic towardOLT 512. Fiber 530 carries the traffic in λ_(u) to filter 522 of OLT512. Filter 522 receives the traffic in λ_(u) and passes the traffic tofilter 516. Filter 516 receives the traffic in λ_(u) and directs thetraffic toward receiver 518. Receiver 518 receives the traffic andprocesses it.

FIG. 4 is a diagram illustrating an example HPON 600 providing extendedreach in the upstream direction according to a particular embodiment ofthe invention. HPON 600 comprises OLT 612, fiber 530, RN 640, and ONUs650. In a similar manner as ONUs 450 of FIG. 2, ONUs 650 provideextended reach by time-sharing transmission of upstream traffic in aplurality of wavelengths, λ₅-λ₈ RN 640 routes this traffic throughmultiplexer 647 (and not through primary power splitter 648). OLT 612receives the traffic at one or more receivers 618. By routing theupstream traffic through multiplexer 647 and not primary power splitter648, the upstream traffic experiences less power loss, therebyincreasing the reach in the upstream direction.

OLT 612 (which may be an example of an upstream terminal) may reside atthe carrier's central office and comprises transmitters 514, multiplexer515, transmitter 520, filter 616, receiver(s) 618, and filter 622.Transmitters 514, multiplexer 515, and transmitter 520 have beendescribed above in conjunction with FIG. 3 and thus will not bedescribed again. It should be noted that, in particular embodiments, OLT412 may also comprise any suitable amplifier (not illustrated) operableto increase the reach of downstream traffic.

Receiver(s) 618 comprise one or more suitable receivers operable toreceive traffic in λ₅-λ₈. In particular embodiments, sets of ONUs 650a-650 d, though transmitting at four different wavelengths λ₅-λ₈,respectively, may time-share transmission of upstream traffic such thatonly a single ONU 650 transmits during a particular time-slot. In suchembodiments, OLT 612 may include a single receiver operable to receivethe traffic in each time-slot, carried in any one of λ₅-λ₈. Althoughupstream bandwidth may not be increased in such embodiments, upstreamreach would be extended.

In alternative embodiments, an ONU 650 of two or more sets of ONUs 650a-650 d may transmit upstream traffic at λ₅-λ₈, respectively, in thesame time-slot, which may be multiplexed at multiplexer 647 of RN 640,as described further below. In such embodiments, OLT 612 may include ademultiplexer (not illustrated) and multiple receivers corresponding toλ₅-λ₈. The demultiplexer may demultiplex λ₅-λ₈ and forward traffic ineach wavelength to a corresponding receiver. In such embodiments,upstream reach would be extended, and upstream bandwidth would also beincreased. However, since upstream traffic may lose additional power atthe demultiplexer in OLT 612, upstream reach may not be as great as inthe case where a single receiver is used at OLT 612 (and traffic in onlyone of λ₅-λ₈ is transmitted per time-slot).

It should be noted that λ₅-λ₈ may (but need not) be the same as λ₁-λ₄transmitted in the downstream direction in FIGS. 3 and 4. Also, λ₅-λ₈may (but need not) be the same as λ₁-λ₄ transmitted in the upstreamdirection in FIG. 2. It should also be noted that, in particularembodiments, receiver(s) 618 and transmitters 514 may be part oftransceivers, and the illustrated PON architecture may be modified inany suitable manner to support such a configuration. It should furtherbe noted that receiver(s) 618 may comprise one or morenon-discriminating, spectrally broadband receivers in particularembodiments. Also, in particular embodiments, any suitable number ofupstream wavelengths may be transmitted, including, for example, aunique upstream wavelength for each ONU 650 (and HPON 600 may bemodified in any suitable manner to support such transmission).

Filter 616 is operable to receive the traffic in λ₁-λ₄ from multiplexer515 and direct the traffic to filter 622. In the upstream direction,filter 616 is operable to receive the traffic in any one or more ofλ₅-λ₈ from filter 622 and direct the traffic to receiver(s) 618. Filter622 is operable to receive the traffic in λ₁-λ₄ from filter 616 and thetraffic in λ_(v) from transmitter 520, combine the traffic, and forwardthe traffic to RN 640. In the upstream direction, filter 622 is operableto receive the traffic in any one or more of λ₅-λ₈ from RN 640 anddirect the traffic to filter 616. Optical fiber 530 has been describedabove in conjunction with FIG. 3 and thus will not be described again.

RN 640 comprises filters 641 and 642, multiplexers 646 and 647, primarypower splitter 648, and secondary power splitters 649 a-649 d. RN 640 isoperable to receive the traffic in λ₁-λ₄ and λ_(v) from OLT 612, filterout and broadcast the traffic in λ_(v), and demultiplex and forward thetraffic in λ₁-λ₄ to the ONUs in corresponding groups ofwavelength-sharing ONUs 650 a-650 d, respectively. In the upstreamdirection, RN 640 is operable to receive the traffic in λ₅-λ₈ from ONUs650 a-650 d, respectively, at multiplexer 647 and forward this trafficto OLT 612. It should be noted that although RN 640 is referred to as aremote node, “remote” refers to RN 640 being communicatively coupled toOLT 612 and ONUs 650 in any suitable spatial arrangement. A remote nodemay also generally be referred to as a distribution node.

Filter 641 may comprise any suitable filter operable to receive adownstream signal comprising traffic in λ₁-λ₄ and λ_(v) and pass thetraffic in λ₁-λ₄ and λλ_(v) to filter 642. In the upstream direction,filter 641 is operable to receive the traffic in λ₅-λ₈ from multiplexer647 and direct this traffic toward OLT 612. Although filter 641 in theillustrated example comprises a single filter, in alternativeembodiments, filter 641 may comprise any suitable number of filters(coupled to optional switches) to facilitate an upgrade of the network(e.g., an upgrade in capacity).

Filter 642 may comprise any suitable filter operable to receive a signalcomprising traffic in λ₁-λ₄ and λ_(v) from filter 641, direct thetraffic in λ₁-λ₄ to multiplexer 646, and direct the traffic in λ_(v) toprimary power splitter 648. In the upstream direction, filter 642 isoperable to receive the traffic in λ₅-λ₈ from primary power splitter 648(and optionally from multiplexer 646) and suitably terminate thistraffic (internally or externally). Alternatively, filter 642 may beoperable to forward the traffic in λ₅-λ₈ to filter 641 where it may besuitably terminated. Although filter 642 comprises a single filter inthe illustrated embodiment, in alternative embodiments, filter 642 maycomprise any suitable number of filters (coupled to optional switches)to facilitate an upgrade of the network (e.g., an upgrade in capacity).

Multiplexer 646 may comprise any suitable multiplexer/demultiplexer (andmay be considered a wavelength router) and is operable to receive thedownstream signal comprising the traffic in λ₁-λ₄ and demultiplex thesignal. Each output port of multiplexer 646 is operable to forward thetraffic in a corresponding one of λ₁-λ₄ to a corresponding secondarypower splitter 649 a-649 d, respectively. In the upstream direction,multiplexer 646 is operable to receive the traffic in λ₅-λ₈ fromsecondary power splitters 649 a-649 d, respectively, and terminate thistraffic (or forward this traffic to filter 642 for suitabletermination).

It should be noted that multiplexer 646 may comprise a cyclicmultiplexer or any other suitable type of multiplexer and may have anysuitable number of ports. Also, although one multiplexer 646 isillustrated in remote node 640, in alternative remote nodes, multiplexer646 may comprise two or more separate multiplexers receiving downstreamsignals from one or more upstream sources and forwarding the trafficdownstream such that ONUs 650 share wavelengths. It should further benoted that the traffic in each wavelength may pass to a differentsecondary power splitter than that illustrated, the traffic in more thanone wavelength may pass to a secondary power splitter, and/ormultiplexer 646 may receive, multiplex, and pass traffic in less or morethan four downstream wavelengths. In particular embodiments, multiplexer646 may be the same as multiplexer 546 of FIG. 3.

Multiplexer 647 may comprise any suitable multiplexer/demultiplexer (andmay be considered a wavelength router) and is operable to receiveupstream traffic in one or more of wavelengths λ₅-λ₈ from secondarypower splitters 649 a-649 d, respectively, and forward the traffic tofilter 641. In particular embodiments, where upstream transmission isbeing time-shared such that only a single ONU 650 transmits during aparticular time-slot, multiplexer 647 receives the traffic in the singlewavelength in the particular time-slot from a corresponding secondarypower splitter 649 and forwards the traffic to filter 641. Inalternative embodiments, where an ONU of two or more sets of ONUs 650a-650 d transmit at λ₅-λ₈, respectively, during a particular time-slot,multiplexer 647 is operable to receive the traffic in the multiplewavelengths in the particular time-slot from a corresponding set ofsecondary power splitters 649, multiplex the wavelengths into onesignal, and forward the signal to filter 641.

In the illustrated embodiment, multiplexer 647 is operable to receiveupstream traffic in λ₅-λ₈ at ports one through four, respectively, fromsecondary power splitters 649 a-649 d, respectively. However, it shouldbe noted that, in alternative embodiments, multiplexer 647 may receiveupstream traffic in any other suitable number of wavelengths and at anysuitable set of ports. For example, in particular embodiments,multiplexer 647 may comprise a cyclic multiplexer or may comprise agreater number of ports. Also, although multiplexer 647 comprises asingle multiplexer in the illustrated embodiment, in alternativeembodiments, multiplexer 647 may comprise two or more separatemultiplexers receiving upstream signals from one or more downstreamsources and forwarding the traffic upstream. Also, multiplexers 646 and647 may comprise a single multiplexer in particular embodiments.

Primary power splitter 648 may comprise any suitable power splitteroperable to receive the traffic in λ_(v) from filter 642 and split thetraffic into four copies. The power of each copy may be less thanone-fourth of the power of the original signal λ_(v). Primary powersplitter 648 is operable to forward each copy to a correspondingsecondary power splitter 649. In the upstream direction, primary powersplitter 648 is operable to receive traffic transmitted by ONUs 650 overλ₅-λ₈ from secondary power splitters 649, combine this traffic into onesignal, and forward the signal to filter 642 for suitable termination.Primary power splitter 648 thus broadcasts downstream traffic in λ_(v)and combines and forwards upstream traffic in λ₅-λ₈ for suitabletermination. Although primary power splitter 648 is illustrated as a 1×4power splitter, any suitable power splitter may be used in alternativeembodiments.

Each secondary power splitter, one of 649 a-649 d, may comprise anysuitable power splitter, such as an optical coupler, operable to receivea copy of downstream traffic in λ_(v) from primary power splitter 648and traffic in a corresponding one of λ₁-λ₄ from multiplexer 646,combine the traffic in λ_(v) and λ₁-λ₄, split the combined traffic intoa suitable number of copies, and forward each resulting copy to acorresponding set of ONUs 650. In the upstream direction, each secondarypower splitter 649 is operable to receive traffic in a corresponding oneof λ₅-λ₈ from each ONU 650 of a corresponding group of downstream ONUs650 and combine the traffic into one signal. For example, secondarypower splitter 649 a is operable to receive traffic transmitted attime-shared λ₁ from ONUs 650 a, secondary power splitter 649 b isoperable to receive traffic transmitted at time-shared λ₂ from ONUs 650b (not illustrated), secondary power splitter 649 c is operable toreceive traffic transmitted at time-shared λ₃ from ONUs 650 c (notillustrated), and secondary power splitter 649 d is operable to receivetraffic transmitted at time-shared λ₄ from ONUs 650 d.

Each secondary power splitter 649 is operable to split the combinedupstream traffic into three copies and forward a first copy to primarypower splitter 648, a second copy to multiplexer 646, and a third copyto multiplexer 647. The copy forwarded to primary power splitter 648, asdescribed above, may be combined with other traffic from other ONUs 650(and later terminated). The copy forwarded to multiplexer 646 may beterminated or forwarded to filter 642 for termination. The copyforwarded to multiplexer 647 may be combined with the copies from othersecondary power splitters 649 in particular embodiments, forwarded tofilter 641, and directed to OLT 612. Although secondary power splitters649 comprise 3×4 couplers in the illustrated embodiment, in alternativeembodiments, secondary power splitters 649 may comprise any othersuitable couplers or combination of couplers (such as a 2×1 couplercoupled to a 2×4 coupler). Secondary power splitters 649 may split orcombine any suitable number of signals and may reside in any suitablelocation in HPON 600.

Each ONU 650 (which may be an example of a downstream terminal) maycomprise any suitable ONU or ONT. Each ONU 650 comprises receivers 562and 572, filters 660 and 670, and transmitter 682. Receivers 562 and 572have been described above in conjunction with FIG. 3 and thus will notbe described again in detail. Each filter 660 may comprise any suitablefilter operable to direct downstream traffic in λ_(v) to receiver 562.Filter 660 is also operable to pass the traffic in a corresponding oneof λ₁-λ₄ to filter 670. In the upstream direction, each filter 660 isoperable to receive the traffic in a corresponding one of λ₅-λ₈ from acorresponding filter 670 and direct the traffic to RN 640.

Each filter 670 may comprise any suitable filter operable to receive thetraffic in a corresponding one of λ₁-λ₄ from a corresponding filter 660and direct the traffic to a corresponding receiver 572. In the upstreamdirection, each filter 670 is further operable to receive the traffic ina corresponding one of λ₅-λ₈ from a corresponding transmitter 682 anddirect the traffic to a corresponding filter 660.

Each transmitter 682 may comprise any suitable transmitter operable totransmit traffic at a corresponding one of λ₅-λ₈ in the upstreamdirection. Transmitters 682 a of ONUs 650 a time-share transmission atλ₅, transmitters 682 b of ONUs 650 b time-share transmission at λ₆ (notillustrated), transmitters 682 c of ONUs 650 c time-share transmissionat λ₇ (not illustrated), and transmitters 682 d of ONUs 650 d time-sharetransmission at λ₈. As discussed above, all ONUs 650 may time-sharetransmission in particular embodiments such that only a single ONU 650transmits in a particular time-slot. In alternative embodiments, an ONU650 a, an ONU 650 b, an ONU 650 c, and/or an ONU 650 d may transmit atλ₁-λ₄, respectively, in the same time-slot.

It should be noted that although four ONUs 650 are illustrated as beingpart of a group of ONUs 650 sharing an upstream wavelength in HPON 600,any suitable number of ONUs 650 may be part of a group sharing anupstream wavelength. It should also be noted that any suitable number ofONUs 650 may be implemented in the network. It should further be notedthat, in particular embodiments, only those ONUs 650 transmitting at aparticular wavelength may be placed downstream of a particular port ofmultiplexer 647, as discussed below in conjunction with FIG. 5.

In operation, in the downstream direction, transmitters 514 a-514 d and520 at OLT 612 transmit traffic at λ₁-λ₄ and λ_(v), respectively.Multiplexer 515 combines the traffic in λ₁-λ₄ and forwards the combinedtraffic to filter 616. Filter 616 receives the traffic in λ₁-λ₄ andforwards the traffic to filter 622. Filter 622 receives the traffic inλ₁-λ₄ from filter 616 and the traffic in λ_(v) from transmitter 520,combines the traffic into one signal, and forwards the signal over fiber530 to RN 640. Filter 641 of RN 640 receives the traffic in λ₁-λ₄ andλ_(v) and forwards the traffic to filter 642. Filter 642 receives thetraffic in λ₁-λ₄ and λ_(v), directs the traffic in λ_(v) to primarypower splitter 648, and directs the traffic in λ₁-λ₄ to multiplexer 646.Primary power splitter 648 receives the traffic in λ_(v) and splits itinto a suitable number of copies. In the illustrated embodiment, primarypower splitter 648 splits the traffic in λ_(v) into four copies andforwards each copy to a corresponding secondary power splitter 649.Multiplexer 646 receives the signal comprising the traffic in λ₁-λ₄ anddemultiplexes the signal into its constituent wavelengths. Multiplexer646 then directs the traffic in λ₁-λ₄ to secondary power splitters 649a-649 d, respectively.

Each secondary power splitter 649 receives a copy of traffic in λ_(v)from primary power splitter 648 and traffic in a corresponding one ofλ₁-λ₄ from multiplexer 646, combines the traffic into one signal, splitsthe signal into a suitable number of copies, and forwards each copy to adownstream ONU 650. In the illustrated embodiment, each secondary powersplitter 649 splits the signal into four copies and forwards the fourcopies to downstream ONUs 450.

In this manner, the traffic (e.g., analog video) in λ_(v) is broadcastto all ONUs 650 and a corresponding one of λ₁-λ₄ is transmitted to andshared by a group of ONUs 650. In the illustrated embodiment, ONUs 650 ashare λ₁, ONUs 650 b (not illustrated) share λ₂, ONUs 650 c (notillustrated) share λ₃, and ONUs 650 d share λ₄. It should be noted that,in alternative embodiments, the groups of ONUs 650 sharing a particularwavelength may be different than those illustrated in FIG. 4, and groupsof wavelength-sharing ONUs 650 may share more than one WDM wavelength.

Filter 660 of each ONU 650 receives a copy of the traffic in λ_(v) and acorresponding one of λ₁-λ₄ from a corresponding secondary power splitter649. Filter 660 then directs the traffic in λ_(v) to receiver 562 (whichthen processes the traffic) and directs the traffic in the correspondingone of λ₁-λ₄ to filter 670. Filter 670 receives the traffic in thecorresponding one of λ₁-λ₄ and directs the traffic to receiver 572 whichthen processes the traffic. Again, since each ONU 650 in a group mayshare one of λ₁-λ₄ with other ONUs 650 in the group, ONUs 650 may applya suitable addressing protocol to process downstream trafficappropriately (e.g., to determine which portion of the traffictransmitted in the corresponding wavelength is destined for which ONU650 in a group).

In the upstream direction, sets of ONUs 650 a-650 d transmit at λ₅-λ₈,respectively. In particular embodiments, as described above, a singleONU 650 transmits traffic in a particular time-slot (and all of ONUs 650time-share time-slots), thereby increasing reach. In alternativeembodiments, an ONU of two or more sets of ONU 650 a-650 d transmits ina particular time-slot (and ONUs of each set time-share time-slots),thereby increasing reach and upstream bandwidth. Thus, in theseembodiments, ONUs 650 a time-share transmission at λ₅ ONUs 650 btime-share transmission at λ₆ (not illustrated), ONUs 650 c time-sharetransmission at λ₇ (not illustrated), and ONUs 650 d time-sharetransmission at λ₈.

Secondary power splitters 649 a-649 d receive the traffic in λ₅-λ₈,respectively. Each secondary power splitter 649 splits the receivedtraffic into three copies and forwards one copy to multiplexer 646, onecopy to multiplexer 647, and one copy to primary power splitter 648.Multiplexer 646 receives a copy of the traffic in λ₅ at a first inputport, a copy of the traffic in λ₆ at a second input port, a copy of thetraffic in λ₇ at a third input port, and a copy of the traffic in λ₈ ata fourth input port, and terminates the traffic (or forwards the trafficto filter 642 for suitable termination).

Multiplexer 647 receives a copy of the traffic in λ₅ at a first inputport, a copy of the traffic in λ₆ at a second input port, a copy of thetraffic in λ₇ at a third input port, and a copy of the traffic in λ₈ ata fourth input port. In the embodiments in which a single ONU 650transmits per time-slot, multiplexer 647 receives the traffic andforwards the traffic to filter 641. In the embodiments in which an ONU650 from two or more sets of ONUs 650 a-650 d transmit at λ₅-λ₈,respectively, in the same time-slot, multiplexer 647 receives thetraffic, combines the traffic, and forwards the traffic to filter 641.

Primary power splitter 648 receives copies of the traffic in λ₅-λ₈ fromsecondary power splitters 649 a-649 d, respectively, combines thetraffic into one signal (when traffic in a plurality of λ₅-λ₈ istransmitted per time-slot), and forwards the traffic to filter 642.Filter 642 receives the traffic in the particular set of λ₅-λ₈ fromprimary power splitter 648 (and optionally from multiplexer 646) andterminates the traffic. Filter 641 receives the traffic in theparticular set of λ₅-λ₈ from multiplexer 647 and forwards the traffic toOLT 612.

Filter 622 of OLT 612 receives the traffic in the particular set ofλ₅-λ₈ and directs the traffic to filter 616. In the embodiments in whicha single ONU 650 transmits per time-slot, filter 616 receives thetraffic in the particular one of λ₅-λ₈ and forwards the traffic toreceiver 618. In the embodiments in which an ONU from two or more setsof ONUs 650 a-650 d transmit at λ₅-λ₈, respectively, in the sametime-slot, filter 616 receives the traffic in the particular set of twoor more wavelengths and forwards the traffic to a demultiplexer (notillustrated). The demultiplexer demultiplexes the wavelengths andforwards the traffic in each wavelength to a corresponding receiver 618.Receiver(s) 618 receive the traffic and processes it.

Modifications, additions, or omissions may be made to the examplesystems and methods described without departing from the scope of theinvention. The components of the example methods and systems describedmay be integrated or separated according to particular needs. Moreover,the operations of the example methods and systems described may beperformed by more, fewer, or other components.

As illustrated in FIGS. 2 and 4 above, upstream traffic may be routed atan RN through a multiplexer, as opposed to a power splitter, to decreasethe power loss experienced by the upstream traffic, thereby extendingreach in the PON. Typical multiplexers can properly receive traffic at aparticular input port in only a certain set of one or more wavelengths.As an example only, a typical 1×4 multiplexer may only be able to directupstream traffic at low loss if the traffic in λ₁ is received at a firstport, the traffic in λ₂ is received at a second port, the traffic in λ₃is received at a third port, and the traffic in λ₄ is received at afourth port. Thus, for proper upstream transmission to take place, eachof the multiplexer's input ports should be connected to downstream ONUsthat transmit at the appropriate wavelength (or set of wavelengths) forthat input port. One challenge that network operators may face whenimplementing a PON that routes upstream WDM traffic through amultiplexer at the RN is notifying whoever is deploying an ONU at aparticular point in the network about the type of ONU that should bedeployed at that point (i.e., the ONU transmitting at the properupstream wavelength).

FIG. 5 is a diagram illustrating an example PON system 700 transmittingoptical markers downstream to indicate proper placement of ONUs 450according to a particular embodiment of the invention. PON system 700comprises WDM marker laser bank 702, splitter 704, and PSPONs 706 a, 706b (not illustrated), 706 c (not illustrated), and 706 d (notillustrated). To indicate proper placement of ONUs 450 in a PSPON 706,WDM marker laser bank 702 transmits a set of marker wavelength signals,at bands λ₅-λ₈, downstream to each PSPON 706. Each downstream markerwavelength signal is routed in each PSPON 706 to different points in thenetwork and corresponds to a particular upstream wavelength that can betransmitted at that point in the network. The type of ONU 450 that canbe deployed at that point in the network is determined based on themarker wavelength signal routed to that point in the network.

WDM marker laser bank 702 may reside at a central office in particularembodiments or in a module external to the central office in alternativeembodiments. Within the central office, WDM marker laser bank 702 mayreside in a module external to OLTs 712 of PSPONs 706 (as illustrated)or on the same OLT card as one or more OLTs 712 in alternativeembodiments. WDM marker laser bank 702 comprises a set of transmitters(not illustrated) operable to transmit at marker wavelength bands λ₅-λ₈.In particular embodiments, these transmitters may be relatively weak(i.e., inexpensive), as the λ₅-λ₈ signals need only act as markers andnot carry traffic in these embodiments. In alternative embodiments,these transmitters may be stronger, and, in particular ones of theseembodiments, traffic may be modulated on the λ₅-λ₈ signals. As describedfurther below, detecting the modulated optical traffic on an opticalmarker signal may be less expensive than detecting the marker wavelengthitself in particular embodiments.

In particular embodiments, traffic modulated on a particular opticalmarker signal may comprise a particular tone that identifies the markersignal itself (e.g., its wavelength), the upstream wavelength thatcorresponds to the marker signal, and/or the ONU type transmitting atthe upstream wavelength corresponding to the marker signal. In theseembodiments, one or more modulators (not illustrated) modulating themarker signal may reside in any suitable location, such as, for example,at laser bank 702. In alternative embodiments, traffic modulated on aparticular marker signal may identify one or more additionalPON-specific characteristics, such as, for example, a particular PON'sOLT identification or any other suitable management information. Inthese embodiments, one or more modulators may modulate the PON-specificcharacteristics on a marker signal for the particular PON. Thesemodulators may reside at laser bank 702, at an OLT 712 of the particularPON itself, or in any other suitable location. It should be noted thatany suitable type of modulation may be used, including, for example,amplitude modulation, frequency/wavelength modulation, and phasemodulation. In addition, a signal may be modulated using one or moretypes of modulation and/or may be modulated one or more times using thesame type of modulation (e.g., using frequency/wavelength modulation).Additionally, modulation may be performed using any suitable deviceand/or technique including, for example, fiber modulation.

In addition to comprising λ₅-λ₈ transmitters, WDM laser bank 702 mayalso comprise a multiplexer or any other suitable combiner operable tocombine λ₅-λ₈ into one signal and forward the traffic to splitter 704.It should be noted that λ₅-λ₈ may (but need not) be the same as λ₁-λ₄transmitted in the downstream direction in FIGS. 3 and 4. Also, λ₅-λ₈may (but need not) be the same as λ₁-λ₄ transmitted in the upstreamdirection in FIGS. 2 and 5 and/or λ₅-λ₈ transmitted in the upstreamdirection in FIG. 4. It should also be noted that, although only fourwavelengths are illustrated, WDM marker laser bank 702 may comprise anysuitable number of transmitters and may transmit at any suitable numberof marker wavelengths. It should further be noted that, in particularembodiments, an amplifier (not illustrated) may be connected to WDMlaser bank 702 to boost the power of the wavelengths.

Splitter 704 may reside at a central office in particular embodiments orin a module external to the central office in alternative embodiments.Within the central office, splitter 704 may reside in a module externalto OLTs 712 of PSPONs 706 (as illustrated) or on the same OLT card asone or more OLTs 712 in alternative embodiments. Splitter 704 comprisesany suitable splitter, such as a coupler, operable to receive the signalcomprising marker wavelengths λ₅-λ₈ from WDM marker laser bank 702 (oroptionally, from an amplifier positioned downstream of WDM marker laserbank 702) and split the signal into four copies. Splitter 704 is furtheroperable to forward each copy of the marker wavelengths to acorresponding downstream PSPON 706.

It should be noted that, in the illustrated embodiment, WDM laser bank702 may be used in conjunction with multiple PSPONs 706 a-706 d for,e.g., cost-sharing purposes. In alternative embodiments, WDM laser bank702 may be used in conjunction with any other suitable number of PSPONs,including a single PSPON 706. In embodiments in which WDM laser bank 702is used in conjunction with a single PSPON 706, splitter 704 need not beused. It should also be noted that PSPONs 706 b-706 d are notillustrated for the sake of clarity and may be similar to PSPON 706 a,which is illustrated.

Each PSPON 706 comprises an OLT 712, optical fiber 430, an RN 740, portmodule 790, identification device 792, and ONUs 450. Each OLT 712comprises transmitter 414, filter 416, receiver(s) 418, transmitter 420,filter 422, and filter 724. Transmitter 414, filter 416, receiver(s)418, transmitter 420, and filter 422 have been described above inconjunction with FIG. 2 and thus will not be described again in detail.It should be noted that, in particular embodiments, OLT 712 may alsocomprise any suitable amplifier (not illustrated) operable to increasethe reach of downstream traffic.

Filter 724 is operable to receive the combined traffic in λ_(d) andλ_(v) from filter 422 and a copy of the signal comprising markerwavelengths λ₅-λ₈ from splitter 704, combine the two signals into onesignal, and direct the signal comprising traffic in λ_(d) and λ_(v) andλ₅-λ₈ to a corresponding RN 740. In the upstream direction, filter 724is operable to receive the traffic in λ₁-λ₄ from the corresponding RN740 and direct the traffic in λ₅-λ₈ to filter 422. It should be notedthat, in alternative embodiments, filter 724 may comprise any othersuitable filter and may be placed in any other suitable location in PON706 a, such as, for example, between filters 416 and 422. Optical fiber430 has been described above in conjunction with FIG. 2 and thus willnot be described again in detail.

Each RN 740 comprises filter 442, multiplexer 446, primary powersplitter 448, filter 741, multiplexer 747, and secondary power splitters749 a-749 d. Filter 442, multiplexer 446, and primary power splitter 448have already been described above in conjunction with FIG. 2 and thuswill not be described again in detail. Filter 741 may comprise anysuitable filter operable to receive the signal comprising traffic inλ_(d) and λ_(v) and λ₅-λ₈ from OLT 712, direct the traffic in λ_(d) andλ_(v) to filter 442, and direct λ₅-λ₈ to multiplexer 747. In theupstream direction, filter 741 is operable to receive the traffic inλ₁-λ₄ from filter 442 and direct the traffic to OLT 712. In particularembodiments, filter 741 may additionally receive upstream traffic inλ₁-λ₄ from multiplexer 747 and terminate the traffic in any suitablemanner.

Multiplexer 747 may comprise any suitable multiplexer/demultiplexeroperable to receive the marker signal in λ₅-λ₈, demultiplex thewavelengths, and forward each marker signal in a correspondingwavelength from a corresponding output port to a corresponding secondarypower splitter 749. Thus, for example, the signal in λ₅ may be forwardedfrom a first port to secondary power splitter 749 a, the signal in λ₆may be forwarded from a second port to secondary power splitter 749 b(not illustrated), the signal in λ₇ may be forwarded from a third portto secondary power splitter 749 c (not illustrated), and the signal inλ₈ may be forwarded from a fourth port to secondary power splitter 749d. In the upstream direction, multiplexer 747 may receive a copy ofλ₁-λ₄ from secondary power splitters 749 a-749 d, respectively, andterminate the traffic (or forward the traffic to filter 741 for suitabletermination in particular embodiments).

It should be noted that, in particular embodiments, multiplexer 747 mayreceive downstream signals in any other suitable number of markerwavelengths (than those illustrated) and may route the marker signalsfrom any suitable set of output ports. For example, in particularembodiments, multiplexer 747 may comprise a cyclic multiplexer or maycomprise a greater number of ports. Also, although multiplexer 747comprises a single multiplexer in the illustrated embodiment, inalternative embodiments, multiplexer 747 may comprise two or moreseparate multiplexers receiving marker wavelengths from one or moreupstream sources and forwarding the traffic downstream. Also,multiplexers 446 and 747 may comprise a single multiplexer in particularembodiments.

Each secondary power splitter 749 may comprise any suitable splitter,such as a coupler, operable to receive a copy of the traffic in λ_(d)and λ_(v) from primary power splitter 448 and a signal in acorresponding one of λ₅-λ₈ from multiplexer 747, combine the two signalsinto one signal, split the signal into a suitable number of copies, andforward each copy to a corresponding downstream ONU 450. In the upstreamdirection, each secondary power splitter 749 is operable to receivetime-shared traffic in a corresponding one of λ₁-λ₄ from a correspondingset of downstream ONUs 450, combine the traffic into one signal, splitthe signal into three copies, and forward one copy to primary powersplitter 448, one copy to multiplexer 446, and one copy to multiplexer447. Although secondary power splitters 749 comprise 3×4 couplers in theillustrated embodiment, in alternative embodiments, secondary powersplitters 749 may comprise any other suitable coupler or combination ofcouplers.

Each port module 790 may comprise any suitable port and/or fiberoperable to couple to an identification device 792 and allowidentification device to identify the marker signal at that point in thenetwork. Port module 790 may also allow the traffic in λ_(d) and λ_(v)to pass in the downstream direction and the traffic in a correspondingone of λ₁-λ₄ to pass in the upstream direction, during regular useand/or while coupled to identification device 792. In particularembodiments, port module 790 may further allow the corresponding markersignal, in one of λ₅-λ₈, to pass in the downstream direction (whenmodule 790 is not coupled to device 792). If the marker signal issufficiently weak, ONUs 450 may receive it without any significantdisruption in reception of λ_(d) and λ_(v) or in transmission of one ofλ₁-λ₄. If the marker signal is not sufficiently weak, a blocking filtermay be placed in any suitable location downstream of port module 790 toblock the marker signal's wavelength (including, for example, in eachONU 450). In particular embodiments, each port module 790 may comprise afilter operable to direct the signal in the corresponding one of λ₅-λ₈toward the port (and not toward the downstream ONU location) and to passthe traffic in λ_(d) and λ_(v) and the corresponding one of λ₁-λ₄.

Each port module 790 may reside in any suitable location in the PSPON706. For example, in the illustrated embodiment, port module 790 iscoupled to a fiber branch upstream to a particular ONU location andreceives the marker signal corresponding to that ONU location. Inparticular ones of these embodiments, port module 790 may comprise abare fiber end or fiber connector (or any suitable tap, as illustrated)at an ONU location that couples to identification device 792 duringtesting, is decoupled from identification device 792 after testing, andthen is coupled to an ONU 450 of the proper ONU type. In alternativeones of these embodiments, port module 790 may comprise a fiber end orconnector (or any suitable tap, as illustrated) remote from an ONUlocation that couples to identification device 792 during testing, isdecoupled from identification device 792 after testing, and then iscoupled to a fiber connector upstream of an ONU location that couples tothe ONU 450 of the proper ONU type. In alternative embodiments, portmodule 790 may be coupled to a plurality of fiber branches (e.g.,branches “a” extending from secondary power splitter 749 a) and mayreceive the marker signal corresponding to ONU locations downstream ofthose fiber branches. In particular ones of these embodiments, portmodule 790 may reside in RN 740.

Identification device 792 may comprise any suitable device operable tobe coupled to port module 790, receive a corresponding marker signal, inone of λ₅-λ₈, and identify the upstream wavelength that should betransmitted by an ONU 450 (or group of ONUs 450) at a correspondingpoint(s) in the network. In particular embodiments, identificationdevice 792 may comprise a stand-alone device that may be coupled to aport module 790. In alternative embodiments, identification device 792may be part of port module 790.

In particular embodiments, identification device 792 may comprise aphotodiode (or any other suitable detector) and exchangeable blockingfilters positionable in front of the photodiode. Based on the blockingfilter from which the marker wavelength is uniquely directed to thephotodiode (or based on the blocking filter from which the markerwavelength is uniquely not directed to the photodiode), identificationdevice 792 may determine the identity of the received marker signal(e.g., its corresponding wavelength), the proper upstream wavelengththat should be transmitted at a corresponding ONU location(s) in thenetwork, and/or the proper ONU type that should be deployed at the ONUlocation(s). In particular embodiments, identification device 792 maythen display the identity of the optical marker signal, the identity ofthe upstream wavelength, and/or the identity of the type of ONUtransmitting at the upstream wavelength.

In alternative embodiments, identification device 792 may comprisemultiple photodiodes (or any other suitable detector) and ademultiplexer configured to route each marker signal to a correspondingphotodiode. Based on what photodiode detects the marker signal,identification device 792 may determine the identity of the receivedmarker signal (e.g., its corresponding wavelength), the proper upstreamwavelength that should be transmitted at a corresponding ONU location(s)in the network, and/or the proper ONU type that should be deployed atthe ONU location(s). In particular embodiments, identification device792 may then display the identity of the optical marker signal, theidentity of the upstream wavelength, and/or the identity of the type ofONU transmitting at the upstream wavelength.

In yet alternative embodiments, identification device 792 may comprise asingle receiver and a processing unit operable to interpret modulationof the marker signal. In these embodiments, each marker signal may bemodulated with a parameter (e.g., a frequency pattern such as a tone)identifying the parameter, the marker signal's corresponding wavelength,the upstream wavelength corresponding to the marker signal, the ONU typetransmitting at the corresponding upstream wavelength, and/or suitablePON-specific characteristics such as, for example, an OLTidentification. In particular embodiments, identification device 792 mayinterpret the modulated parameter and display the identity of theparameter, the identity of the marker signal's corresponding wavelength,the identity of the upstream wavelength corresponding to the markersignal, the identity of the ONU type transmitting at the correspondingupstream wavelength, and/or the identity of any suitable PON-specificcharacteristic. In alternative embodiments, each marker signal may bemodulated with data traffic identifying the marker signal'scorresponding wavelength, the upstream wavelength corresponding to themarker signal, the ONU type transmitting at the corresponding upstreamwavelength, and/or suitable PON-specific characteristics. In particularof these embodiments, identification device 792 may display the identityof the optical marker signal, the identity of the upstream wavelength,the identity of the type of ONU transmitting at the upstream wavelength,and/or the identity of any suitable PON-specific characteristic. Inalternative embodiments, the proper upstream wavelength that should betransmitted at a particular point in the PSPON (i.e., the proper ONUtype) may be identified in any other suitable manner.

As discussed above, in particular embodiments, identification device 792may comprise a stand-alone device that can be plugged and unplugged fromthe PSPON 706. In particular ones of these embodiments, an ONU deployermay carry identification device 792 and use device 792 at any portmodule 790 in any PSPON 706 to determine the ONU type that should bedeployed at a corresponding ONU location. Thus, for example,identification device 792 may be used to determine that ONUs 450 a(transmitting upstream traffic at λ₁) should be deployed downstream offiber branches “a” when a marker signal in λ₅ is detected at port module790 a, that ONUs 450 b (transmitting upstream traffic at λ₂) should bedeployed downstream of fiber branches “b” when a marker signal in λ₆ isdetected at port module 790 b (not illustrated), that ONUs 450 c(transmitting upstream traffic at λ₃) should be deployed downstream offiber branches “c” when a marker signal in λ₇ is detected at port module790 c (not illustrated), and that ONUs 450 d (transmitting upstreamtraffic at λ₄) should be deployed downstream of fiber branches “d” whena marker signal in λ₈ is detected at port module 790 d. In particularembodiments, identification device 792 need not disrupt the trafficbeing transmitted in the PSPON (besides the marker wavelength) whilecoupled to PSPON 706.

ONUs 450 have been described above in conjunction with FIG. 2 and thuswill not be described again. However, it should be noted that, inparticular embodiments, ONUs 450 may receive a corresponding markersignal during use (when the marker signal is not being tested by anidentification device 792). In such embodiments, reception of traffic inλ_(v) and λ_(d) and transmission of traffic in a corresponding one ofλ₁-λ₄ will not be distorted provided that the marker signal is ofsufficiently low power. If not, each ONU 450 may comprise a blockingfilter to block the marker wavelength (or, alternatively, a blockingfilter may be placed in any suitable location upstream of the ONU). Itshould also be noted that, in particular embodiments, ONUs 450 of FIG. 5may use pre-amplifiers to increase the power of upstream signals.

It should be noted that WDM marker laser bank 702 need not be used totransmit markers in an HPON that transmits multiple downstream andupstream, WDM wavelengths, such as, for example, in HPON 600 of FIG. 4.Assuming that the downstream and upstream wavelengths correspond to thesame sets of ONUs, a deployer of ONUs may identify the type of ONU todeploy at a particular ONU location by identifying the downstream WDMwavelength being received at that location. Where downstream andupstream wavelengths are asymmetrical in an HPON, network operators mayoptionally continue to use WDM marker laser bank 702 to transmitmarkers. It should also be noted that, in particular embodiments, aparticular PSPON 706 may be upgraded to an HPON, such as, for example,to HPON 600 of FIG. 4. In particular ones of such embodiments, WDM laserbank 702 may be disconnected from any other PSPONs 706, and thetransmitters in WDM laser bank 702 may be reused as downstreamtransmitters in the HPON.

In operation, in the downstream direction, transmitters at WDM laserbank 702 transmit marker signals at wavelengths λ₅-λ₈, and a multiplexerat WDM laser bank 702 combines the signals into one signal and forwardsthe combined signal to splitter 704. Splitter 704 receives the signal,splits the signal into four copies, and forwards each copy to acorresponding PSPON 706.

At PSPON 706 a, transmitters 414 and 420 transmit traffic at λ_(d) andλ_(v), respectively. Filter 416 receives the traffic in λ_(d) anddirects the traffic to filter 422. Filter 422 receives the traffic inλ_(d) from filter 416 and the traffic in λ_(v) from transmitter 420,combines the two signals into one signal, and forwards the combinedsignal to filter 724. Filter 724 receives the copy of marker signals inλ₅-λ₈ from splitter 704 and the traffic in λ_(d) and λ_(v) from filter422, combines the two signals into one signal, and forwards the combinedsignal to RN 740 a over fiber 430.

At RN 740 a, filter 741 receives the marker signals in λ₅-λ₈ and thetraffic in λ_(d) and λ_(v) from OLT 712 a, directs the marker signals inλ₅-λ₈ to multiplexer 747, and directs the traffic in λ_(d) and λ_(v) tofilter 442. Filter 442 receives the traffic in λ_(d) and λ_(v) fromfilter 741 and directs the traffic to primary power splitter 448.

Multiplexer 747 receives the marker signals in λ₅-λ₈, separates thesignals, and forwards each signal in a particular wavelength to acorresponding secondary power splitter 749. Primary power splitter 448receives the traffic in λ_(d) and λ_(v), splits the traffic into fourcopies, and forwards each copy to a corresponding secondary powersplitter 749.

Each secondary power splitter 749 receives the signal in a correspondingone of λ₅-λ₈ from multiplexer 747 and a copy of the traffic in λ_(d) andλ_(v) from primary power splitter 448, combines the two signals, splitsthe combined signal into four copies, and forwards each resulting copydownstream to a corresponding port module 790 a. Each port module 790 areceives the marker signal comprising a corresponding one of λ₅-λ₈ andthe traffic in λ_(d) and λ_(v), directs the marker signal toidentification device 792 when device 792 is coupled to port module 790,directs the marker signal to the downstream ONU 450 or ONU location (orblocking filter) when device 792 is not coupled to port module 790, anddirects the traffic in λ_(d) and λ_(v) to the downstream ONU 450 or ONUlocation (if an ONU has not yet been deployed).

When identification device 792 is coupled to port module 790,identification device 792 receives the marker signal and determines theidentity of the marker signal (e.g., its corresponding wavelength), theidentity of the upstream wavelength that can be transmitted at acorresponding ONU location, and/or the ONU type that can be deployed atthat location. In particular embodiments, identification device 792interprets modulation of the marker signal to identify a modulatedparameter corresponding to the marker signal, the upstream wavelengththat can be transmitted at a corresponding ONU location, the ONU typethat can be deployed at that location, and/or any PON-specificcharacteristic. Identification device 792 may display one or more ofthese results. An ONU 450 of the particular ONU type may then bedeployed at the corresponding ONU location.

Once deployed, an ONU 450 may receive the traffic in λ_(d) and λ_(v) atfilter 460, and filter 460 may direct the traffic in λ_(v) to receiver462 and the traffic in λ_(d) to filter 470. Receiver 462 then receivesand processes the traffic in λ_(v). Filter 470 receives the traffic inλ_(d) and directs the traffic to receiver 472, which receives andprocesses the traffic in λ_(d).

In the upstream direction, sets of ONUs 450 a-450 d transmit at λ₁-λ₄,respectively. In particular embodiments, a single ONU 450 transmitstraffic in a particular time-slot (and all of ONUs 450 time-sharetime-slots), thereby increasing reach. In alternative embodiments, anONU of two or more sets of ONUs 450 a-450 d transmit in the sametime-slot (and ONUs of each set time-share time-slots), therebyincreasing reach and upstream bandwidth. Thus, in these embodiments,ONUs 450 a time-share transmission at λ₁, ONUs 450 b time-sharetransmission at λ₂ (not illustrated), ONUs 450 c time-share transmissionat λ₃ (not illustrated), and ONUs 450 d time-share transmission at λ₄.

Each port module 790 receives the traffic in a corresponding one ofλ₁-λ₄ from a downstream ONU 450 and directs the traffic to acorresponding secondary power splitter 749. Secondary power splitters749 a-749 d receive the traffic in λ₁-λ₄, respectively. Each secondarypower splitter 749 splits the received traffic into three copies andforwards one copy to multiplexer 446, one copy to multiplexer 747, andone copy to primary power splitter 448.

Multiplexer 446 receives a copy of the traffic in λ₁ at a first inputport, a copy of the traffic in λ₂ at a second input port, a copy of thetraffic in λ₃ at a third input port, and a copy of the traffic in λ₄ ata fourth input port. In the embodiments in which a single ONU 450transmits per time-slot, multiplexer 446 receives the traffic andforwards the traffic to filter 442. In the embodiments in which an ONUof two or more sets of ONUs 450 a-450 d transmit in the same time slotat λ₁-λ₄, respectively, multiplexer 446 receives the traffic, combinesthe traffic, and forwards the traffic to filter 442.

Multiplexer 747 receives a copy of the traffic in λ₁ at a first inputport, a copy of the traffic in λ₂ at a second input port, a copy of thetraffic in λ₃ at a third input port, and a copy of the traffic in λ₄ ata fourth input port and terminates the traffic (or forwards the trafficto filter 741 for suitable termination). Primary power splitter 448receives copies of the traffic in λ₁-λ₄ from secondary power splitters749 a-749 d, respectively, combines the traffic into one signal (whentraffic in a plurality of λ₁-λ₄ is transmitted per time-slot), andforwards the traffic to filter 442.

Filter 442 receives the traffic in the particular set of λ₁-λ₄ frommultiplexer 446 and directs the traffic to filter 741. Filter 442 alsoreceives the traffic in the particular set of λ₁-λ₄ from primary powersplitter 448 and terminates this traffic in any suitable manner. Filter741 receives the traffic in the particular set of λ₁-λ₄ from filter 442and forwards the traffic to OLT 612. Filter 741 may also suitablyterminate any traffic it receives from multiplexer 747.

Filter 724 of OLT 612 receives the traffic in the particular set ofλ₁-λ₄ from RN 740 and directs the traffic to filter 422. Filter 422receives the traffic in the particular set of λ₁-λ₄ from filter 724 anddirects the traffic to filter 416. In the embodiments in which a singleONU 450 transmits per time-slot, filter 416 receives the traffic in theparticular one of λ₁-λ₄ and forwards the traffic to receiver 418. In theembodiments in which an ONU in two or more sets of ONUs 450 a-450 dtransmit in the same time-slot at λ₁-λ₄, respectively, filter 416receives the traffic in the particular set of two or more wavelengthsand forwards the traffic to a demultiplexer (not illustrated). Thedemultiplexer demultiplexes the wavelengths and forwards the traffic ineach wavelength to a corresponding receiver 418. Receiver(s) 418receives the traffic and processes it.

Modifications, additions, or omissions may be made to the examplesystems and methods described without departing from the scope of theinvention. The components of the example methods and systems describedmay be integrated or separated according to particular needs. Moreover,the operations of the example methods and systems described may beperformed by more, fewer, or other components.

Although the present invention has been described with severalembodiments, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present invention encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A method for transmitting optical markers in apassive optical network (PON) system, comprising: transmitting a firstoptical marker signal, the first optical marker signal modulated toinclude information identifying an optical network unit (ONU) typeconfigured to transmit at an upstream wavelength corresponding to thefirst optical marker signal; transmitting a second optical markersignal, the second optical marker signal modulated to includeinformation identifying an ONU type configured to transmit at anupstream wavelength corresponding to the second optical marker signal;at a distribution node of the PON, routing the first optical markersignal to a first set of one or more optical fibers in the PON, eachoptical fiber corresponding to a first upstream wavelength; at thedistribution node of the PON, routing the second optical marker signalto a second set of one or more optical fibers in the PON, each opticalfiber corresponding to a second upstream wavelength; receiving eitherthe first marker signal or the second marker signal at a locationdownstream of the distribution node, the location being a location atwhich an ONU is not coupled to the PON; determining an ONU typeidentified in the received marker signal; and coupling an ONU to the PONbased on the determined ONU type.
 2. The method of claim 1, wherein eachoptical fiber is associated with a particular ONU location of the PON atwhich an ONU may be coupled.
 3. The method of claim 1, wherein eachoptical fiber is associated with a plurality of ONU locations of thePON.
 4. The method of claim 1, wherein each optical fiber is configuredto couple to an identification device configured to identify at leastone of an upstream wavelength corresponding to the first optical markersignal and an ONU type transmitting at the upstream wavelengthcorresponding to the first optical marker signal.
 5. The method of claim1, further comprising: combining the first optical marker signal and thesecond optical marker signal into one signal; splitting the signalcomprising the first optical marker signal and the second optical markersignal into a plurality of copies; and forwarding each copy comprisingthe first optical marker signal and the second optical marker signal toa corresponding PON of a plurality of PONs.
 6. The method of claim 1,further comprising modulating at least one of the first optical markersignal and the second optical marker signal to include managementinformation of the PON.
 7. An identification device configured to: becoupled to any one of a plurality of optical fibers of a passive opticalnetwork (PON) when an optical network unit (ONU) is not coupled to anONU location, each optical fiber corresponding to at least one ONUlocation of the PON at which an ONU may be coupled; receive an opticalmarker signal of a set of optical marker signals from the coupledoptical fiber, the optical marker signal modulated to includeinformation identifying an ONU type configured to transmit at anupstream wavelength corresponding to the optical marker signal; andidentify the ONU type configured to transmit at the upstream wavelengthcorresponding to the optical marker signal by interpreting themodulation on the optical marker signal.
 8. The identification device ofclaim 7, further configured to display at least one of the identity ofthe upstream wavelength corresponding to the optical marker signal andthe identity of the ONU type transmitting at the upstream wavelengthcorresponding to the optical marker signal.
 9. A method for using anidentification device, comprising: coupling the identification device toany one of a plurality of optical fibers of a passive optical network(PON), each optical fiber corresponding to at least one optical networkunit (ONU) location of the PON, the identification device being coupledto the ONU location when an ONU is not coupled to the ONU location;receiving an optical marker signal of a set of optical marker signalsfrom the coupled optical fiber, the optical marker signal modulated toinclude information identifying an ONU type configured to transmit at anupstream wavelength corresponding to the optical marker signal; andidentifying at least one of the upstream wavelength corresponding to theoptical marker signal and the ONU type transmitting at the upstreamwavelength corresponding to the optical marker signal by interpretingthe modulation on the optical marker signal.
 10. The method of claim 9,further comprising displaying at least one of the identity of theupstream wavelength corresponding to the optical marker signal and theidentity of the ONU type transmitting at the upstream wavelengthcorresponding to the optical marker signal.